In the trench filling process, it is essential to obtain such parameters as the step depth of the trench after etching back the polysilicon (POLY) for process monitoring of the electronic device, e.g. TRENCH POWER MOS et al.
One way to obtain the depth of the step is to slice. Specifically, one wafer is selected from a plurality of wafers, then it is sliced along a direction vertical to the trench, and the depth of the trench is obtained by using microscope and other related equipments.
Another conventional approach is implemented by monitoring a test pattern. Briefly speaking, a test area with respect to the normal manufacturing area is formed during the manufacturing process. The test area has the same trench as the normal manufacturing area, and the required parameters is obtained by determining the relevant parameters of the trench in the test area.
If the width of the test pattern (i.e. the trench) is too small, the surface profilometry may not able to acquire correct scanning parameters, if the width is too large, the polysilicon will grow into a shape with a higher sidewall and a lower middle portion due to the filling feature of the ploysilicon in the trench, such that the surface profilometry may also not able to obtain the correct result. Accordingly, due to the limitation of the width of the test pattern, the current test pattern can not be too wide, while the surface profilometry can not obtain the correct scanning parameters under the current width.